Bringing the Starshade to Reality

by Paul Gilster on November 20, 2009

The goal of detecting a terrestrial class exoplanet has burned bright in the imagination ever since the discovery of the first planets orbiting main sequence stars. In a recent SEED Magazinestory, Lee Billings (one of the most graceful science writers now working) harkens back to then NASA administrator Daniel Goldin’s 1996 speech at the American Astronomical Society meeting in San Antonio, Texas. Goldin talked about seeing Earth-like exoplanets up close, speculating that in 25 years we might be able to obtain images with a resolution to see clouds, continents and oceans.

I’m going to use a different Goldin quote than Lee did, from a later speech, but the idea is clear enough in either iteration. Here Goldin is speaking about the classrooms of the mid-21st Century and what they might look like:

When you look on the walls, you see a dozen maps detailing the features of Earth-like planets orbiting neighboring stars. Schoolchildren can study the geography, oceans, and continents of other planets and imagine their exotic environments, just as we studied the Earth and wondered about exotic sounding places like Bangkok and Istanbul . . . or, in my case growing up in the Bronx, exotic far-away places like Brooklyn.

This is a classroom I’d love my grandchildren to spend some time in, but exactly which generation gets to do that depends on how timely we are in creating the kind of terrestrial planet finder missions that can do the job. With a star outshining a terrestrial exoplanet by a huge factor, the challenge of just finding the planet is, as Billings notes, “…like photographing a lit match on the cusp of a detonating hydrogen bomb.” And in any case, we seem to have set up a built-in generational gap here. We’re making huge progress today at detecting exoplanets, but funding for the follow-up investigative tools is sadly lacking.

This is why I’ve often looked at starshade concepts on Centauri Dreams, thinking the technology of an external occulter could simplify the detection process and, in doing so, lower the costs of the project. Webster Cash (University of Colorado at Boulder) has spent the last five years working on a starshade that could function with the upcoming James Webb Space Telescope. The cost: $700 million to image alien Earths around nearby stars, a fraction of the price of the original TPF-C and TPF-I concepts worked up at the Jet Propulsion Laboratory.

We’re not talking about those Goldin-style images of Earth-like worlds on the schoolhouse wall, at least, not with the earliest generation of starshade. But Cash does believe we can use the early starshades to get a spectrum of an Earth-like exoplanet within the next ten years. That could flag the presence of oceans and even reveal signs of life.

Here’s Billings’ description of the operative technology:

Cash’s starshade would resemble a many-petaled sunflower—if sunflowers were matte-black and about half a football field in diameter. Its special shape is designed so that waves of starlight will diffract around it, lapping against and nullifying each other to cast an ultra-dark shadow, ensuring that only an exoplanet’s light falls on the JWST’s huge mirror. Equipped with small thrusters, the starshade would fly some 70,000 kilometers in front of the JWST, precisely aligning to block light from a target star so that its accompanying planets could be seen.

Read the article for more on this (and, if you’re looking for further background, run a search on this site for stories on Cash’s work). And keep this in mind. Astro2010 is a decadal survey of astrophysicists put together by the National Research Council, one that will soon release a report on research priorities for the coming decade. Cash’s starshade has been submitted to the committee, and so has a competing starshade concept by David Spergel and Jeremy Kasdin (Princeton University), former Cash collaborators. Will the committee support a starshade?

The lack of support from NASA on bringing such projects home is a natural consequence of the funding crisis the agency faces, one that may or may not change no matter what the upcoming Astro2010 report has to say. “The problem here is not the technology, but the lack of money to demonstrate it one way or another — and there’s something wrong with that,” Cash tells Billings. “This wouldn’t be just helping me, it would be NASA helping itself. NASA has a unique opportunity to conduct an experiment whose results, if positive, will never be forgotten.”

Goldin was an administrator with vision:
“When you look on the walls, you see a dozen maps detailing the features of Earth-like planets orbiting neighboring stars. Schoolchildren can study the geography, oceans, and continents of other planets and imagine their exotic environments”.

That is also my own dream!

Regarding JWST and a starshade:
“The cost: $700 million to image alien Earths around nearby stars, a fraction of the price of the original TPF-C and TPF-I concepts worked up at the Jet Propulsion Laboratory.
(…) Cash does believe we can use the early starshades to get a spectrum of an Earth-like exoplanet within the next ten years.”

Wow, it would be sooo short-sighted not to fund an initiative like this (about the price of a long weekend warfare in Iraq)!
I would almost ask: how can we donate to this privately?

BTW, up to which distance (in ly) would this concept work for detection and spectroanalysis of earthlike planets?

In my opinion, the best way to solve the cash issue is to eliminate manned space missions for the forseeable future. Yes, I know a lot of people would be disappointed in this, but if you look at the situation pragmatically, detecting life bio-signatures on another world for a modest cost would far outweigh any perceived science benefit we would get by returning to the moon.

Even more important, by eliminating the manned space effort NASA could prioritize a mission to Europa where there is a reasonably good chance for finding some form of life. According to the current NASA plan, we won’t get there until at least 2027 and that’s only an orbital mission to search for habitable conditions, not life itself. I’m 59 years old now and I’ll be long dead before NASA actually sends a mission that looks for life on this promising world. Needless to say, I’m extremely frustrated at NASA’s priorities! What could possibly be more important than discovering life on another world?

Re: volume that the JWST/occulter combo will be able to survey… I think it’s optimistic to say this would work out to 10 parsecs, which often seems to be the standard distance mentioned for the first generation of space-based direct-imaging missions. More realistically, it might be limited to only the nearest 10 stars or so. But this is just my immediate and perhaps faulty recall from the interviews — I don’t have time at the moment to check the transcripts. Someone like Web Cash or Jeremy Kasdin could of course speak much more authoritatively.

$700M is like $2 or $3 per taxpayer. I probably lose that much down the couch every year. Also agree that in our current situation we should be prioritizing probes over manned spaceflight. And don’t even get me started on Iraq etc.

In order to justify the added Government Funding for this critical research area perhaps the place to start is to do a complementary Study to the new ICARUS project that would seek to answer in detail the question where should we go and how should we develop the data base to determine this?
For the next couple of hundred years, unless there is some sort of radical technology breakthrough, it is probably safe to say that our maximum direct exploratory radius from our Sol/Terra system is about 60 Light Years. Therefore, perhaps we should seek to build support for a comprehensive “Affordable Near Sol/Terra Survey Program” that would seek to survey and characterize everything out to 60 Light Years from Sol/Terra including Mars size exo-planets, and even habitable moons using a combination of technologies, techniques and programs including the Webster Cash occulters as well as projects to exploit the effects of Gravitational Lensing.

The idea here is to set a high but achievable goal (6o light year survey by 2025) using known technologies, and then conduct a Systems Engineering Study to determine the optimum mix of fully integrated technologies, techniques, and programs to cost-effectively execute this very worthy, but constrained goal.

A famous Systems Developer who sold large scale programs to the U.S. Government for years once defined Systems Engineering as “practical solutions to real world problems”. Instead of trying to sell this or that program such as TPF to the Government to explore exo-planets we needs a big goal with a big vision that comes with a big but constrained problem to be solved. Then the scientific community needs to show the U.S. Government that it has done its homework in terms of coming up with a practical roadmap and plan to get there if funded.

I would argue that for purposes of “doability” the total pricetag should not exceed $10 Billion to achieve our 60 Light Year Survey by 2025 using a combination of integrated technologies, techniques and programs that will provide the best comprehensive data set to answer the basis survey question “what is out there?”. Essentially, what the Scientific community would be advocating for is “full Space Situational Awareness” out to 60 Light Years from planet Earth and this would not only include exo-planet surveys and searches for Brown Dwarfs etc, etc, but also Asteroid and Comet characterization in our own Solar System as well. This way the nation would be buying both protection of planet Earth from potential dangerous near Earth Objects and great Science at the same time. This is an approach that can effectively compete for dollars as the U.S. Government sets it priorities. The other trick of course is to make sure that the integrated “Affordable Near Sol/Terra Survey Program” has the optimum mix of technologies, techniques and programs to maximize the number of well paying jobs across the country in key Congressioal Districts.

Nice plan Ken. Best thing is if the USA decides to go with it, then starts vacillating, other countries might jump in for the sake of prestige and to make a statement that the USA has become decadent. That might shame the powers-that-be back into the game.

Cutting all manned program efforts is a stupid idea chiefly because cutting funding to it makes it harder to justify the space science program. The two go hand-in-hand in the public, and Congressional, mind. Maybe big showy rides to the Moon are fiscally troublesome, but some kind of development needs to be occurring to show everyone that space is about their future, not just “gee whiz” moments doled out by scientists from their ivory tower.

In my opinion, the best way to solve the cash issue is to eliminate manned space missions for the forseeable future.

Wrong. Abandoning manned space missions will send a signal that we no longer see the expansion of mankind into space as a real possibility. If men stop seeing space as their destiny, the interest in its scientific exploration will completely fade. And the cash that politicians are willing to give away, with it. Abandon the manned spaceflight, and the budget of NASA will be reduced by far more than the amount of money saved by that. (most probably progressively reduced to zero).

There is only one way to solve the lack of money. Bigger budget. Preferably big enough to make manned missions to do also something more than just flying there and back.

I have a very naïve, probably stupid, question. Would it be possible to use a naturally occurring occulter? Say, have a telescope that is able to manoeuvre into position behind asteroids and planets within out solar system and then “take a shot”?

tesh, JWST has neither enough fuel nor strong enough thrusters to do such a big trip. And also, asteroids and planets tend to have mass large enough to force the spacecraft to constantly adjust its position, which is problematic because all thrusters can introduce vibrations and blur the picture, and also, the fuel will be spent quite swiftly. Man made star shade can be made lighter than the telescope itself, so it is quite less fuel expensive.

In terms of scientific bang per buck, probes are much more efficient than manned missions. From that perspective it makes sense to give probes priority.

Not sure the public is really any more interested in manned missions than they are in probes. Probably I live in a rather unenlightened area, but I know few people who have any interest in space exploration at all.

I am not against human space flight, but, for the last 40 years it has been squandering money in LEO without any thought for the future. Specifically, the question of what to do next after the expensive space station has been given little though. What was really needed was the development of a proper propulsion system to be developed so that we could be ready for interplanetary exploration.
Instead we have nothing. VASIMIR might still save us, but it will need a nuclear source of energy and that will take years, just to overcome the politics of it.
The targets for human flight proposed by the Augustine commission are a joke : a flyby of Venus ? Are you serious and what for ? similarly for the rest.
If we had developed a decent propulsion system we could go to Mars where human exploration could still make some sense, at least for a while.
I’m saying for a while because, as time passes, a human mission to Mars makes less and less sense. I don’t believe it can happen before 2035+. By then robotics will be so advanced that Spirit and Opportunity will look like toys. I don’t want to make forecast on AI, but I am sure that robots in 2035 will be a lot more autonomous and capable of meaningful exploration.
The problem is that a human mission to Mars will still cost $100B in today’s $ in 2035+ while the robotic mission will still cost only $700M.
As the robots get better the human mission makes less and less sense.
So, human space flight has completely lost the edge for exploration and the more time passes, the more so. The problem here is that machines get better every day while people are still the same.
There is still scope for human space flight as a more long term goal to expand in the solar system and beyond. I believe that this is essential for long term survival but I’m pretty sure that human exploration is over. Robots are order of magnitudes cheaper and constantly improve.

If the public were not interested in space, then NASA would be dismantled long ago.

In terms of scientific bang per buck, probes are much more efficient than manned missions. From that perspective it makes sense to give probes priority.

Only in short term, and for low budget missions. If you have enough money to pay for the fixed cost of manned missions, any cent above that will yield far more science than one spent on a similar robotic mission. For example, even a mediocre geologist is capable of doing in 5 minutes more than a robotic mars rover in a week.

Till they get to completely autonomous multi exaflops computers with < 30 watt power consumption, like the mark 1 brain you have between your ears, It will take surely more than 25 years.

And humans don't need to stay the same. Now, you need at least 13 KPa pressure pure oxygen. Genetically engineered humans could spend half an hour in pure vacuum just by holding their breath and may have breathing muscles strong enough to need only a gas mask without a spacesuit. They can be made more radiation resistant than robots, all that while needing orders of magnitude less power.

And, anyway, I am not willing to give my future away to robots, because if the "robots are getting better, so who needs humans at all" argument holds for space, it holds also for earth, and humans, and biological life in general would be phased out down here as well.

Till they get to completely autonomous multi exaflops computers with &lt 30 watt power consumption, like the mark 1 brain you have between your ears, It will take surely more than 25 years.

And humans don’t need to stay the same. Now, you need at least 13 KPa pressure pure oxygen. Genetically engineered humans could spend half an hour in pure vacuum just by holding their breath and may have breathing muscles strong enough to need only a gas mask without a spacesuit. They can be made more radiation resistant than robots, all that while needing orders of magnitude less power.

And, anyway, I am not willing to give my future away to robots, because if the “robots are getting better, so who needs humans at all” argument holds for space, it holds also for earth, and humans, and biological life in general would be phased out down here as well.

Enzo, I believe manned spaceflight as it currently exists within NASA’s program is wasteful. But I fully believe that a permanently established Moon base would be a huge step forward for technology development.

A Moon base is the first step towards developing the technology for self sufficiency in the Solar System and beyond, as we develop and deploy the means to mine lunar soil, process it, and manufacture infrastructure from it.

The Moon offers opportunities not available nearby elsewhere. Among them are: Low gravity for launch of spacecraft loaded and fueled with payloads derived from the Moon; Zero atmosphere allowing no drag on space launches; Zero atmosphere for very large telescopes;

I intended my comments on probes vs. manned missions mainly for space beyond the Moon. There’s certainly a case to be made for radio telescopes on the far side of the Moon (shielded from Earth’s radio noise). But as for optical telescopes, doesn’t the Moon have a two-week “day”? Plus (on the near side) a rather bright object in the sky during the night?

Bryan, NS,
A base on the moon might be part of the long term goal of expanding in the solar system. I’m a bit concerned that expenditure could get out of hand like in the space station and one is left with a base with only two people in it that are just enough to look after the base itself.
As for the telescopes on the moon, I remember reading someting about the nasty dusty environment.
Speaking of telescopes, Herschel cost 850 M euros. How much more would have cost if it were an optical telescope ?
Wouldn’t it be worth having a 3.5 m optical telescope to substitute Hubble for that little money ?
I have seen estimates for each shuttle lunch of up to $1.3B each if one takes into account the cost of the whole program and divides by the number of launches. It seems a lot easier than fixing Hubble. Where am I wrong ?

Finally, what I’d really hate is if some of the recent low science proposals like the human flyby of Venus, humans to Lagrange etc. would get in the way of something as simple and brilliant like Cash’s star shade (because of funds diversion).
Or something not as simple but just as brilliant like follow up missions to Europa and Titan.

T_U_T,
You do not need to be completely autonomous to be an effective explorer: these things are not going to Aplha Centauri where help is at least 8 years away.

You might have noticed that I make no forecast of true AI. I do not know if/when it’ll happen. However, I’m pretty sure that robots in 2035 will be capable of walking a around without a team of engineers planning their every move for a day in advance. They will be able to detect that they are getting stuck *before* they do. They will also be able to detect something new and stop moving to investigate. They will be capabl eof recognizing some geological formations.
They will still be directed by scientists from Earth but they will not need as many engineers and support. Their best advantage is that their cost will stay the same or even drop in real terms.
Put in another way, you can have a few people for a few weeks or months on the surface of Mars for, probably, $100B or so or, for a similar price, you can have 100-200 of the things above roaming Mars for a few years.

I assumed pricing similar to Spirit and Opportunity, economy of scale could make it better. And of course, you would need 100-200 of them, you could save the money for similar but more expensive endeavors to Europa, Titan and Enceladus.

One final question : given that Spirit and Opportunity have happily survived on Mars for so long, isn’t the next, nuclear powered robot a bit over engineered ? After all nuclear power is difficult, especially politically and all that seems to be needed on the next robot is a brush to clear the solar panels to be attachable to the robotic arm. Just a thought.

So you are stuck with a solar powered nonautonomous robot. That pretty much restricts you to lander missions to mercury, moon mars and asteroids. ( no one needs to land on earth, and venus lander can not be solar driven anyway ).
And you are still stuck with a robot that can, at best, do in a day what a human geologist could do in a few minutes.

No gas giant missions or beyond, because you would need the dreaded N word thing to get any power that far from the sun.

And no, you can not really save any money by mass producing a rover. Because for each world you have to design another one, a mars rover would not work on mercury or moon. a moon rover would not work on mars. a mercury rover would be an overkill on ceres., etc. And the major cost is the rocket anyway. And by sending one and the same rover to the same world, you will face diminishing science returns pretty soon, so you are not going anywhere that way.

I thought that it was pretty clear that the discussion was about Mars. Solar power was only in that context. Nuclear power is essential, especially for propulsion. The economy of scale would have come by building 100-200 Mars rovers. And in fact I said that you would not need 100-200 rovers for Mars, you can have a lot less there and use the money to launch other robotic missions.

The question is : use $100B to one mission with a few people for a few months in one location or sampling 100-200 points on Mars for years for the same money.
Or better, rather than spending your $100 B all on Mars, you could have a large variety of missions in the solar system.
Herschel was 850 M euro, Cassini $3.25 B, etc. You’d get a variety of missions, including some sample returns from Mars, Titan and Europa orbiter +landers, Neptune orbiter, a large space telescope with Cash planet imager, Venus ultraviolet adsorber analysis, Enceladus plume sample return, etc. etc. If don’t know if that would also be enough to design a nuclear reactor (non RTG) to power VASIMIR propulsion. If not you can delete some of the missions above because a decent propulsion system is needed by everyone humans and robots alike.
Simply no contest with a single human mission to Mars.

Enzo, this is exactly the kind of short term thinking that I warned against. You compare missions, like they were an one time event that has no effect on the next mission.
Completely ignoring the fact, that for example nuclear drive developed for manned missions will make next manned mission much cheaper, and if you ask for money for development of nuclear drive for an unmanned mission, you will not get it, because unmanned probe can go there even without it.
Completely ignoring the fact that a permanent research colony on mars will produce orders of magnitude more science than even thousand one shot rovers.

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last nine years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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